Typical commercial flat roof construction often consists of steel joists spaced apart with corrugated metal roof deck spanning between the steel joists. Rigid insulation is glued on top of the corrugated roof deck and a rubber roof is applied on top of the rigid insulation as waterproofing. In 15% of buildings constructed in this manor, a concrete slab is placed on top of the corrugated metal roof before the rigid insulation is placed as a means of providing a code required fire rating to the roof assembly. When a concrete slab is poured it releases water vapor as it cures and hardens. This curing process can continue for over a month. However the rigid insulation and final finished rubber roof is applied on top of the concrete slab before the curing process is complete. The top of the concrete slab is sealed off by applied rigid insulation and rubber roof. The bottom of the concrete slab is sealed off by the continuous corrugated metal roof spanning between steel joists.
The moisture trapped inside the concrete slab as it continues to cure tries to escape the slab but can not. This trapped moisture can cause premature failure of the rigid insulation adhesive between the slab and the insulation. This trapped moisture can infiltrate the rigid insulation reducing its R value. This trapped moisture can also affect the bond of the rubber roofing reducing the life expectancy of the rubber roofing.
A solution to this trapped moisture is illustrated and detailed in prior art documented in U.S. Pat. No. 3,498,015 patented Mar. 3, 1970 by P. A. Seaburg ET AL—Poured Gypsum Roof Structure with Lower Vent Means for Removing Excess Moisture.
This prior art solved the issue of trapped moisture in a concrete roof slab by providing vent slots in the bottom of the corrugated steel deck valleys. A wicking material is placed in the corrugated steel deck valleys before the concrete is poured to absorb the moisture from the concrete. The wicking material can then release the trapped moisture to the building space below through the vent slots in the bottom of the valleys.
Roof construction using vented roof deck with wicking materials in the valley's of the corrugated steel vented roof deck has improved moisture removal from concrete poured on top of steel roof decks and covered on top with rigid insulation and rubber roofing, but experience has shown that premature failure of the rubber roofing adhesive and rigid insulation is still occurring that is attributed to excess moisture retained in the concrete slab.
It is therefore an objective of our invention to provide a method of roof construction using existing construction materials to increase the surface area air exposure on the bottom of slabs poured on top of corrugated steel roof deck to promote more efficient evaporation of moisture from the slab.
Expanded metal lath is a metal mesh currently used as a base for stucco wall construction on the exterior of buildings. The lath consists of gauge metal sheets that are perforated in a regular pattern. The sheets are then stretched to open up the perforations creating a pattern of small openings in the gauge metal sheets. The openings in the lath equates to 70% or more of the surface area of a finished sheet. The size of the holes are proportioned such that concrete will penetrate the holes slightly but will not pass through the holes.
Our invention is a method for using expanded metal lath as a form laid on top of corrugated metal roof deck to prevent a cementitious slab poured on top of a metal roof deck from entering the corrugations of the roof deck creating spaced apart mini air ducts out of each of the metal roof deck valleys. The mini air ducts consist of the two sides and one bottom of the valley of each corrugation of the metal roof deck and the op consists of the poured concrete slab in combination with the expanded metal lath form spanning across the corrugations.
Alternatively stucco mesh can also be manufactured of twisted wire mesh as opposed to expanded metal lath. This manufactured product can be substituted equally for expanded metal lath in this invention.
Sheet metal tek screws are sheet metal screws used to join two overlapping corrugated metal deck panels together. The tek screws have a drill bit tip to create the proper size hole through two lapped layers of gauge metal deck. The threaded shaft of the tek screw then draws together the two layers of lapped gauge metal deck. The head of the tek screw acts as a washer and a stop when the proper penetration is achieved.
A sheet metal tek screw would not be used to attach overlapping layers of expanded metal lath. The lath already has expanded holes in it. The threaded shaft of the tek screw would not properly engage the lath and would not draw together two layers of expanded metal lath.
Our invention uses sheet metal tek screws, normally used for connecting two layers of gauge sheet metal together, to connect together expanded metal lath lapped on top of corrugated roof deck. Sheet metal tek screws would be threaded through a hole in the expanded metal lath then drilled through the gauge metal corrugated roof deck. The threaded shaft of the tek screw would draw the screw down through the corrugated roof deck. The head of the tek screw acts as a washer and a stop to pinch the expanded metal lath down onto the corrugated roof deck. Sheet metal tek screws would be spaced at regular intervals to hold the expanded metal lath in place over the corrugations of the metal roof deck forming the tops of mini air ducts preventing concrete from flowing into the corrugations of the roof deck.
Metal roof deck can be ordered with vent slots in the horizontal gauge metal bottom of each valley. Vent slot openings can total up to 6% of the area on the bottom of each deck valley bottom. In contrast the expanded metal lath openings total 70% or more of the area on the metal lath. Under the previous art, air flow is limited to the 6% slot openings that are blocked by either concrete poured directly into the corrugated metal deck valleys or the wicking material laid in the valleys. Under our invention, with the metal deck valleys unblocked by concrete or wicking material, air can flow freely into the valleys of the metal roof deck. Differential temperature between the topside of the roof construction and the underside of the roof construction will naturally promote air movement through the unblocked vent slots. The air will move across the expanded metal lath with concrete poured on top. 70% openings expose more area on the bottom of the concrete slab to the drying effects of air flowing across the concrete slab.
Alternatively, corrugated metal roof deck is sometimes ordered with no vent slots. Providing expanded metal lath with 70% openings will not remove excess moisture from the concrete slab if air is blocked from flowing through the mini ducts formed in the valleys of the corrugated roof deck. Vent holes can be added to the valleys of the corrugated roof deck with a standard electric powered wheel grinder.
Our invention is a construction method where one rib of a corrugated metal deck between two valleys is cut by holding a grinder 45 degrees off vertical. The cut is perpendicular across the rib and 45 degrees down the sides of the adjacent valleys leaving the bottom of the valleys uncut. The wheel grinder is then rotated 90 degrees to −45 degrees off vertical. The two cuts join together just above the uncut valley bottom creating a rectangular hole in the top of the rib and two triangular holes in adjacent sides of the valleys. The rectangular hole in the rib is covered by the expanded metal lath that forms the top of the mini ducts and does not contribute to air flow in the mini ducts. The two triangular side holes in the adjacent sides of the valleys allow air to flow through the mini ducts and can replace the air flow normally provided by corrugated metal deck vent slots. This procedure can be repeated at regular intervals to provide the required area of venting equivalent to the venting area normally provided by corrugated metal roof deck with vent slots.